An active high-entropy air electrode for enhanced reversible solid oxide cell performance and stability

The insufficient stability and poor surface reaction kinetics (i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) of air electrodes are significant factors hindering the development of reversible solid oxide cells (R-SOCs). The high-entropy strategy offers a new direction to optimize air electrodes. We introduce a high-entropy air electrode, (La 0.12 Pr 0.12 Nd 0.12 Sm 0.12 Gd 0.12 )Sr 0.4 Co 0.2 Fe 0.8 O 3− δ (LPNSGSrCF), demonstrating a low polarization resistance (0.15 Ω cm 2 ) and good durability (1.3×10 −3 Ω cm 2 h −1 ), superior to those of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ (0.31 Ω cm 2 , 2.0×10 −3 Ω cm 2 h −1 ) at 650 °C. The elevated activity may be a result of the substantial concentration of oxygen vacancies and rapid reaction kinetics, as verified by X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and distribution of relaxation times studies. Specifically, an R-SOC with LPNSGSrCF air electrode achieves a peak power density of 1.05 W cm −2 in fuel cell mode and a current density of −0.89 A cm −2 at 1.3 V in electrolysis cell mode (with 30% H 2 O) at 700 °C. Moreover, the cells with LPNSGSrCF electrode can be stably operated in both modes for over 100 h. A novel high-entropy material with a formula of (La 0.12 Pr 0.12 Nd 0.12 Sm 0.12 Gd 0.12 ) Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LPNSGSrCF) has been designed for R-SOCs. The cells with LPNSGSrCF air electrode demonstrate exceptional electrochemical performance and operational stability under intermediate-temperature conditions.